A proton therapy treatment table

Researchers confirm proton therapy results in fewer side effects for many cancers


Published: Jun 7, 2019 at 01:36 PM EDT

In the largest side-by-side comparison study of its kind, proton therapy for cancer treatment was found to have fewer side effects while maintaining similar survival rates when compared to traditional x-ray radiation therapy.

The study, led by Washington University School of Medicine in St. Louis and the Perelman School of Medicine at the University of Pennsylvania,  included almost 1,500 patients receiving combined chemotherapy and radiation therapy for lung, brain, head & neck, gastrointestinal, and gynecologic cancers that were localized to one part of the body and had not metastasized.    A combination treatment of chemotherapy and radiation therapy is a standard treatment leading to cure for many non-metastatic cancers.  However, it is common for patients of this treatment regimen who receive traditional radiation to experience severe side effects that can significantly reduce quality of life and in some cases require hospitalization, trading cure for side effects.

Proton therapy is an advanced form of radiation therapy that uses protons to deliver the radiation directly to the tumor.  Protons are positively charged particles with unique physical characteristics that allow more of the radiation dose to be directly deposited at the tumor.  There is minimal entrance dose and no exit dose, significantly reducing radiation received to nearby healthy tissue and organs when compared to x-ray therapy. Traditional radiation therapy uses photons which travel all the way through the body and pass through healthy tissue on the way out.  Both proton and x-ray radiation therapy are FDA approved.

Results of the study

After controlling for differences between the groups, such as age and additional medical problems, researchers found that proton therapy patients experienced a two-thirds reduction in the relative risk of severe side effects within 90 days of treatment compared to x-ray therapy patients.

“We looked at grade-three side effects, including pain or difficulty swallowing, difficulty breathing, nausea, or diarrhea, among others, often severe enough for patients to be hospitalized,” says the study’s lead author Brian Baumann, an adjunct assistant professor of radiation oncology in the Perelman School of Medicine and an assistant professor of radiation oncology at Washington University School of Medicine in St. Louis. “Our clinical experience is that concurrent chemoradiation therapy patients treated with protons, rather than photons, tend to have fewer side effects. While there is some literature supporting that finding for several disease sites, we did not expect the magnitude of the benefit to be this large.”

Furthermore, the researchers found no difference between the two groups in survival, suggesting that proton therapy is equally effective in treating cancer and it causes fewer side effects.  Overall survival at one year for the proton therapy group was 83 percent of patients versus 81 percent for the x-ray radiation therapy group.



  1. Baumann BC, Mitra N, Harton JG, Xiao Y, Wojcieszynski AP, Gabriel PE, Zhong H, Geng H, Doucette A, Wei J, O’Dwyer PJ, Bekelman JE, Metz JM. Comparative effectiveness of proton therapy versus photon therapy as part of concurrent chemo-radiotherapy for locally advanced cancer. American Society of Clinical Oncology poster session. June 1, 2019.